From: Of James Bottomley
> Sent: 22 June 2015 18:36
> To: Alan Stern
...
> > > Obviously, for a disk with a writeback cache that can't do flush, that
> > > window is much wider and the real solution should be to try to switch
> > > the cache to write through.
> >
> > I agree. Doing the switch manually (by writing to the "cache_type"
> > attribute file) works, but it's a nuisance to do this when you have a
> > portable USB drive that gets moved among a bunch of machines.
>
> Perhaps it might be wise to do this to every USB device ... for external
> devices, the small performance gain doesn't really make up for the
> potential data loss.
What about systems running from USB memory/disk directly plugged into the
motherboard and shut inside the case?
Since they shouldn't be removed you don't want to bypass any write cache.
(Any more than you'd want to on a real disk.)
There is an additional problem caused by very temporary USB disconnects
(easily caused by electrical noise causing (probably) Vbus to bounce).
In these conditions you don't want to signal a USB remove at all - at
least not to the filesystem - until the device has remained disconnected
for a short time.
David
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